State of the art automatic transmissions, especially for automobiles, comprise planetary sets, which are shifted by means of friction elements and shift elements, like clutches and brakes, and are generally and selectively connected with a sliding start-up element having a bypass clutch, like in the case of a hydro-dynamic torque converter or a flow-based clutch.
Such automatic transmissions are known, for instance, through the filing of DE 199 49 507 A1, of a multi-step transmission, in which, at the drive shaft, two non-switchable front end gear sets are provided, which generate two rotational speed values on the output side, which, beside the drive shaft's rotational speed, can electively be shifted to a double planetary set in a manner, through selective engagement of the applied shift elements, so that in the case of shifting to the next higher gear or lower gear, only one shift element of the both just activated shift elements have to be enabled or disabled. Through the use of five shift elements, seven forward gear positions are being achieved, through the use of six shift elements, nine or ten forward gear positions.
In addition, known through DE 102 13 820 A1, is a multi gear automatic transmission with eight forward gear positions and one reverse gear position, comprising a first input path T1 of a first gear ratio, an input path T2, having a larger gear ratio as this input path T1, a planetary gear set of the Ravigneaux type with four elements, whereby the four elements comprise a first element, a second element, a third element, and a fourth element, in that order, is the content of a rotational speed diagram; a clutch C-2, which transfers rotation of the input path T2 to the first element S3; a clutch C-1, which transfers rotation from the input path T2 to the fourth element S2; a clutch C-4, which transfers rotation from the input path T1 to the first element; a clutch C-3 which transfers rotation from the input path T1 to the second element C3; a brake B-1, which establishes engagement of the fourth element; a brake B-2, which establishes engagement of the second element; and an output element, which is linked with the third element S3.
A nine-gear multi step transmission is also known in the art through DE 29 36 969 A1; it comprises eight shift elements and four gear sets, whereby one gear set serves as an intermediate gear, the main transmission features a Simpson set and an additional gear set as reverse transmission.
Additional multi step transmissions are known in the art, as an example, from the applicant DE 102005010210 A1 and DE 102006006637 A1.
Transmissions which are automatically switchable, based on planetary design, are generally and often described in the art and undergo continuous further development and improvements. These transmissions should present minimal effort in the assembly, include a small number of shift elements, and should avoid during sequential shifting the possible double shift, so that, during shifting in defined gear groups, just one shift element will be changed at a time.
Known to the applicant, from the non-published DE 102008000428.3, is a multi-step transmission of a planetary design, comprising an input drive and an output drive, which are arranged in a housing. The known transmission includes at least four planetary gear sets, named herein as first, second, third, and fourth planetary gear set, at least eight rotatable shafts—named herein as drive shaft, output shaft, third, fourth, fifth, sixth, seventh, and eighth shaft—as well as at least six shift elements, comprising brakes and clutches, whose selective engagement causes different gear ratios between the input and the output, so that preferably nine forward gear positions and one reverse gear position are feasible.
Hereby, the first and second planetary gear set, preferably designed as minus-planetary sets, exhibit a switchable intermediate wheel set, whereby the third and the fourth planetary set are a main wheel set.
In the known multi-step transmission, it is provided that the carriers of the first and second planetary gear set are coupled to each other via the fourth shaft, which is connected to an element of the main gear set; that the ring gear of the first planetary gear set is coupled to the sun gear of the second planetary gear set via the eighth shaft, which can be detachably connected via a first clutch with the driveshaft; and that the sun gear of the first planetary gear set can be coupled by means of the third shaft via a first brake to a housing and can be detachably connected via a second clutch with the driveshaft, in which case the ring gear of the planetary gear set can be coupled by means of the fifth shaft via a second brake to a housing of the transmission. In addition, the seventh shaft is permanently connected to at least one element of the main transmission and can be coupled via a third brake to a housing of the transmission, in which case the sixth shaft is permanently connected with at least one additional element of the main gear set and can be detachably connected via a third clutch with the driveshaft; the output shaft is permanently connected to at least one additional element of the third gear set.
In the known transmission, the fourth shaft is preferably permanently connected to the ring gear of the planetary gear set, in which case the sixth shaft is permanently connected to the ring gear of the fourth planetary gear set and the carrier of the third planetary gear set, and can be detachably connected via the third clutch to the driveshaft. In addition, the seventh shaft is permanently connected to the sun gears of the third and fourth planetary gear set and can be coupled via the third brake to a housing of the transmission. The output is supplied by means of the output shaft being permanently connected to the carrier of the fourth planetary gear set. In addition, the third and fourth planetary gear can be combined into, or, as the case may be, reduced to a Ravigneaux set with a common carrier and a common ring gear.